ObjectiveThe goal of this exercise is to correctly demodulate the noisy
received signal in RxOQPSK.mat.

Signal Constellation
The transmitted data points are taken from the signal space
constellation below. The four points are equally spaced on a
circle with radius A and are simply the four possible ordered pairs [
±A/sqrt(2), ±A/sqrt(2) ]. Each
transmitted signal carries two
information bits, as shown below.

After being corrupted by noise, the received signal is demodulated by
the system below, which detects the transmitted signal space points and
outputs the estimated values of the transmitted bits.Design Exercise

Part I: OQPSK Transmitter

Using blocks from the SIMULINK Block Library, the Signal Processing
Blockset, and the Communications Blockset, design an OQPSK modulator,
patterned after the one shown above, to meet the following
specifications:

For the delay, you can use the Delay block located at Signal Processing
Blockset --> Signal Operations --> Delay. For the purposes
of your design, you can omit the bit sequence and the
look-up tables (LUTs), and just use two "Signal From Workspace" blocks
as inputs to the system.

Part II: OQPSK Detector

Using blocks from the
SIMULINK Block Library, the Signal Processing
Blockset, and the Communications Blockset, design an OQPSK detector
that is compatible with the
modulator from Part I. The structure of the demodulator is shown
in Figure 5.4.8 in the text. I recommend sampling the matched
filter outputs at 2 samples per symbol and using every other sample on
I and Q, as suggested by Figure 5.4.8. You can output these
samples to the Matlab workspace
and implement the decision logic in a post-processing fashion using a
Matlab script.

[ Sanity Check ]You can test your designs from Parts I and II by connecting the
output of your modulator to the input of your detector. Use the
same data source as in the Binary PAM exercise
(the Signal from Workspace block), except that you need separate
sources for each arm in the modulator. Set the input to these
sources such that you modulate the symbol pattern [00 01 10
11]'). In your project
window, go to the menu Simulation --> Configuration Parameters and
set the parameters to:

Note: The 4 corresponds to
the number of transmitted symbols, the first 1
corresponds to the delay of the downsample operation in the detector,
the second 1 corresponds to the delay in the Q arm, and the 8 is the
number of samples per symbol.

When you have
successfully debugged your
system, you are ready for the final part of the exercise.

Part III: Detecting an
Unknown Data SetHere are the steps for the final
part of the exercise:

Connect the input of your detector to a From File
block and set the filename toRxOQPSK.mat (If you have problems with that
file,
here is a ZIP version).

The last 119 values of
the sampled matched filter outputs represent 34 ASCII characters.
Determine the message using your own conversion script or an ASCII
table, such as the one found here.

Submit your answer AND
your detector model file (.mdl SIMULINK file) to the class TA via the
Digital Drop Box in Blackboard (you may submit via e-mail only if you
have
problems with Blackboard). You should organize your files into a
folder, and then ZIP the folder and submit the ZIP file. The
naming
convention for the ZIP file is "Lab#_YourLastName.zip."

Plot the eye diagram
and signal space projections. You may submit these
electronically, or turn them in at the beginning of the next class
period after the due date.